1. Field of the Invention
The present invention relates to a superconducting multilayer electrode for use in the high-frequency bands of microwaves, decimillimetric waves, or millimetric waves, various devices using superconducting multilayer electrodes, such as high-frequency transmission lines, high-frequency resonators, high-frequency filters or high-frequency devices, and a method of producing such electrode, more specifically a method of setting a film thickness of such superconducting multilayer electrode.
2. Description of the Related Art
In the high-frequency bands of microwaves, decimillimetric waves, or millimetric waves, it is preferable that electronic parts, such as cavity resonators or dielectric resonators using each mode of TEM, TE, and TM, be made small and light in weight by using high-dielectric constant materials, as well as that conductor loss be decreased to obtain a high no-load Q. Energy loss of a high-frequency device can be broadly classified into conductor loss due to a skin effect and dielectric loss due to a dielectric material. In recent years, dielectric materials which have a low-loss characteristic, though they have a high-dielectric constant, have been developed and put into practical use. Therefore, the conductor loss is more dominant than the dielectric loss in the no-load Q of the circuit. To solve this problem, Japanese Patent Laid-Open No. 6-310900 disclose a multilayer electrode in which dielectric layers and thin-film conductor layers are alternately laminated.
When superconducting materials are used in electrodes or shielding conductors of electronic parts, such as cavity resonators or dielectric resonators using each mode of TEM, TE, and TM, the superconductor is preferable because the electrical resistance of the superconductor is zero, and its surface resistance is small.
When the superconductor is placed in an electromagnetic field, supercurrent flows on the surface of the superconductor, making it possible to prevent the penetration of the electromagnetic field. However, when the electromagnetic field becomes strong and the supercurrent exceeds the critical current density, the superconductor becomes a normal conductor and is no longer a superconductor. Therefore, it is necessary to use the superconductor at a critical current density or smaller. This critical current density makes the upper limit of the resistance to electric power of electronic parts low to such an extent as being too low from a practical standpoint. Also, this fact causes a technological difficulty of applying superconducting materials to practical devices in the microwave and millimetric wave bands.